256 SUMMARY OF MEASUREMENTS. Chap. VII 



with various surrounding species. The seeds sown at 

 the same time in a garden have generally been matured 

 daring the same season and in the same place ; and in 

 this respect they differ much from the seeds sown by 

 the hand of nature. Some exotic plants are not 

 frequented by insects in their new home, and there- 

 fore are not intercrossed ; and this appears to be a 

 highly important factor in the individuals acquiring 

 uniformity of constitution. 



In my experiments the greatest care was taken that 



in each generation all the crossed and self-fertilised 



plants should be subjected to the same conditions. 



Not that the conditions were absolutely the same, for 



the more vigorous individuals will have robbed the 



weaker ones of nutriment, and likewise of water when 



the soil in the pots was becoming dry ; and both lots 



at one end of the pot will have received a little more 



light than those at the other end. In the successive 



generations, the plants were subjected to somewhat 



different conditions, for the seasons necessarily varied, 



and they were sometimes raised at different periods of 



the year. But as they were all kept under glass, they 



were exposed to far less abrupt and great changes of 



temperature and moisture than are plants growing out 



of doors. With respect to the intercrossed plants, theil 



first parents, which were not related, would almosl 



certainly have differed somewhat in constitution ; and 



such constitutional peculiarities would be variously 



mingled in each succeeding intercrossed generation, 



being sometimes augmented, but more commonly 



neutralised in a greater or less degree, and sometimes 



revived through reversion ; just as we know to be the 



case with the external characters of crossed species and 



varieties. With the plants which were self-fertilised 



during the successive generations, this latter important 



